1. Field of the Invention
This invention concerns a focus improver for concave reflecting surface of a circular cross section. It also relates to an application of such improver for solar energy collection.
2. Description of the Prior Art
It is well known that a parabolic reflecting surface provides the optimum concentration of parallel rays. Similarly, the laws of optics teach that parallel rays reflected from circular surfaces will not focus at a common location, but rather will form a caustic of the reflected light rays instead of a common focal location. Such optical results of reflections from a spherical surface is known as spherical abberation and, where the concave reflecting surface is cylindrical, it would be termed cylindrical aberration. However, the elimination of the aberration created by a circular surface has heretofore necessitated the use of a parabolic surface, and fabrication of such parabolic surface is much more difficult and costly than a circular type surface.
A compound concentration lens system has been proposed for use with a solar energy collector system. For example, a known system employed a compound concentration lens system for concentrating solar rays, in addition to a series of prism-type light transmission sections on the edges of the lens for directing the sun's rays to a central location. That system required passage of the sun's rays through the lens and prism sections in order to reach the focal location. The known system is described in U.S. Pat. No. 4,022,186 Northrup, Jr., dated May 10, 1977.
On the other hand, a concave reflector structure has the advantage over a lens type system that it is easier and less costly to make and also that it causes no absorption of the sun's rays such as would be involved in a lens type system. Consequently, it is an object of this invention to provide a focus improver for a concave reflector that has a circular cross section.
Another object of the invention is to provide an application of a focus improver, according to the foregoing, which will result in an improved solar energy collector that is relatively inexpensive and yet quite efficient.